1. Field of the Invention
The present invention relates to bushings, which are extensively used in a variety of assemblies within automobiles, particularly in suspension systems. More specifically, the present invention relates to a sectioned composite bushing having directionally variable dampening properties. In addition, the inventive bushing is characterized by inner and outer cylindrical collars bridged by circumferentially arranged elastomeric sections. The inventive bushing attenuates vibration and noise transmitted through metal structures.
2. Description of the Background Art
In today's automotive industry, extensive time and effort has been expended to reduce vibration, and vibration and friction-induced noise in vehicles, while improving ride comfort and vehicle handling. Technologically refined vibration isolators and resilient bushings have been developed to achieve better vibration isolation and noise control, and are commonly employed between interrelated structural components. A number of bushings are known in which a resilient annular cylinder is fitted between two coaxial sleeves. The resilient annular portion of the bushing permits components of a suspension system that are connected to the inner sleeve and the outer sleeve, respectively, to move toward and away from each other in the radial direction with respect to the bushing axis, while the elastomeric portion dampens the initial harshness of the motion.
Preferably, the elastomeric member is designed to permit a large deflection in the radial direction, so that the elastomeric material can absorb large loads or shocks, without damaging the surrounding components. However, deflection of the bushing in the axial direction is undesirable, because such deflection causes axial spreading and consequent misalignment of the suspension system components. Axial deflection also has adverse effects upon the bushing, since it tends to weaken the mechanical bond between the compressed elastomeric member and the respective inner and outer sleeves.
Typically, this type of known bushing includes at least two concentric rigid cylindrical collars (sleeves) with an annular elastic member interposed between them. The inner sleeve is securely connected to one structural component, while the outer sleeve is secured to another structural component. Generally, the sleeves are formed of metal, while the annular elastic member is of a flexible, resilient material such as rubber. In the automotive industry, such resilient bushings are incorporated in frames and others parts to dampen the dynamic vibration of metal structures. They are also utilized to generate high noise impedance in what might otherwise be an all-metal path for the transmission of structure-borne sounds in a metal structure.
A few illustrative examples of previously known resilient composite bushings are described in U.S. Patents issued to Hadano et al., Johnson et al., Tsuiki et al., and Hein.
In U.S. Pat. No. 6,474,631, Hadano et al. discloses a cylindrical stabilizer bushing with a main body elastic rubber member. The rubber elastic member has a radially layered structure comprising an inner rubber layer having with high sliding properties and an outer rubber layer integrally laminated on the outer surface of the inner layer rubber. This construction allows vulcanized bonding of the inner sliding rubber portion to the outer, main body rubber portion, even if the sliding rubber portion material is injected when the vulcanization of the main body rubber portion is almost complete.
In U.S. Pat. No. 6,419,230, Johnson et al. reveal a suspension bushing with a sleeve. The sleeve member includes an inner surface and a cavity. A core member is disposed inside the cavity. In addition, two elastomeric members are also disposed inside the cavity. The first elastomeric member is positioned adjacent to the core, while the second elastomeric member is interposed between the first elastomeric member and the inner surface. The first elastomeric member has a modulus that is greater than that of the second elastomeric member, so that one of the elastomeric members absorbs low frequency vibration, while the other elastomeric member absorbs high frequency vibration. As seen in the previous reference, an outer elastomeric member is concentrically surrounding an inner elastomeric member.
Tsuiki et al., in U.S. Pat. No. 5,984,283, disclose a stabilizer bushing for use as component of a vehicle suspension system. The subject bushing is provided with a vibration damping main body. This main body comprises a resilient, thick-walled cylindrical body, formed of rubber, which defines a stabilizer bushing. The resilient body is obtained by inserting a rubber cylindrical inner body into a rubber cylindrical outer body. The outer body acts as a main part of the resilient rubber body. The inner surface of the inner rubber body has high sliding characteristics, and acts as a slide surface that is adapted to hold a stabilizer bar.
In the U.S. Patent to Hein (U.S. Pat. No. 5,224,790), a bushing assembly with axial restraint properties is disclosed. The bushing assembly of Hein includes an outer sleeve encircling an inner sleeve that contacts a stabilizer bar. The outer sleeve is formed of a more flexible material than the inner sleeve. The nesting sleeves are designed to restrain axial movement, while allowing ease of rotational movement. The outer sleeve engages and at least partially surrounds an inner sleeve. The inner sleeve is designed to surround and engage a metal stabilizer bar. The engagement of the stabilizer bar by the inner sleeve is designed to inhibit relative axial movement between the stabilizer bar relative and the inner sleeve. The inner diameter of the inner sleeve includes a high-friction surface, such as knurling, or even an adhesive engagement of the inner sleeve to the stabilizer bar.
Primarily, the known background art, including the references cited herein, use concentrically disposed and radially stacked concentric layers of elastomeric material to provide composite bushings. Although the reference patents teach combining rubber materials of differing resiliency to offer an improved bushing, which results in improved vehicle comfort and handling, they achieve this goal by providing concentric layering of elastomeric components in a radial direction. However, when the composite is formed in this configuration and is placed under a radial load, one layer of rubber with a particular resiliency transfers its unique physical attributes to radially adjacent layer(s) of a different resiliency.
Hence, the bushings disclosed in the references are unable to derive the benefits from the attributes of one particular layer having a specific resiliency, because of the interdependence with the other radially disposed layer(s) having a different resiliency. Since each of the bushings described above uses a structure composed of elastic materials of differing elasticities radially disposed in concentric layers, the dampening effect they provide is a result of the combined elasticities of the layers. Controlling the resulting damping effect can be difficult.
A composite bushing is needed that optimally uses a plurality of elastic elements of differing elasticities, disposed in such a manner that the physical characteristics of one elastic element can be experienced substantially independently of the influence of adjacent elastic elements. A composite bushing is needed wherein the resiliency is directionally dependent, such that the bushing provides a plurality of elasticities, wherein a specific resiliency is associated with a specific direction of applied load. A composite bushing is needed that, when used to attenuate vibration and transmitted noise in an automotive assembly, provides improved vehicle handling and ride comfort.